1. Field of the Invention
This invention relates to attenuators which are particularly adapted for the absorption of energy in the event of an impact between an errant vehicle and a second, typically stationary or slow-moving vehicle, in the hope of minimizing injury to the occupants of both vehicles, and, more specifically, to trailer-mounted crash attenuators.
2. Description of the Related Art
Truck mounted attenuators (TMA's) have been in use for many years. TMA's typically comprise a fixed backup mounted to a dump truck or other vehicle and an energy absorbing cartridge attached to the fixed backup. In some TMA's, the cartridge is attached to the fixed backup via a hinge to allow for rotation of the cartridge to a vertical orientation for transport. The TMA cartridge absorbs the impact of an errant vehicle that collides with it, thereby protecting the truck, the vehicle, and the occupants of both.
One important purpose for the TMA's deployed on trucks and other vehicles, typically those used in highway construction, is for protecting workers in those vehicles. The trucks equipped with TMA's are referred to as shadow vehicles, barrier vehicles, and advance warning vehicles. Shadow vehicles are moving trucks that effectively block errant vehicles in the flow of traffic from striking the workers directly ahead of the truck. The protected workers typically perform mobile activities, such as crack pouring, patching utility work, striping, coning, pavement repair, pavement marking, and delineator repair, and the shadow vehicle moves with and behind the workers. Barrier vehicles are effectively used to protect vehicles in the flow of traffic from a hazardous situation, such as blocking open excavations. The barrier vehicles may be unoccupied. Advance warning vehicles may be used to warn the drivers in the flow of traffic of an upcoming moving or stationary situation. An example of an advance warning vehicle is a truck in a lane of a highway displaying an arrow indicating that the lane is closed ahead and that vehicles in the lane need to start to merge into another lane.
Under current federal highway safety regulations, all TMA's used on the National Highway System must be tested and approved based on one of three test levels: 25 mph TL-1, 45 mph TL-2, and 62.5 mph TL-3. If a TMA is tested and approved for the higher test speeds, it is automatically approved for all lower speed levels. To obtain product approval two mandatory tests are required. The differences between the two tests are that one test requires the use of an 1800 lb impact vehicle and the other test requires the use of a 4400 lb impact vehicle. The requirement to pass the tests is to collect two data points which record the forces exerted on the occupant in the impacting vehicle. The first data point is to record the force the occupant receives during the impact event, which must not exceed 20 G. This is defined as being the equivalent as 20 times a persons weight exerted on the occupant during the impact event. The second data point is occupant velocity, which is the forward head speed at which the impacting vehicle's occupant moves forward during the impact event and comes into contact with the steering wheel. The survival threshold value has been found to be 12 m/s (26.84 mph), so at no time during the impact event can the occupant velocity exceed the survival threshold of 12 m/s.
Mobile Impact Truck Attached Attenuators (MITAA) such as the Scorpion® TMA, available from the present assignee, TrafFix Devices, Inc., are attached directly to the truck frame. U.S. Pat. No. 6,581,992, which is co-assigned with the present application to TrafFix Devices, Inc., describes the SCORPION TMA, and the '992 patent is herein expressly incorporated by reference, in its entirety. Attaching the impact attenuator to the truck frame provides the strongest point to support a 2000 LB attenuator and the large forces that occur during an impact event. Attaching directly to the truck frame also requires skilled labor such as welders and machinists, and can typically take up to three days to complete the assembly and install the more complicated attenuators on the market today. The demand for a greater cost effective method of installation and ease of attachment has been identified by TMA manufacturers. As a result, TMA manufacturers have developed a line of Mobile Impact Truck Attached Attenuators (MITAA) which attach directly to a truck's pintle hook, rather than the frame.
The challenge of attaching an attenuator to the pintle hook is to prevent the attenuator from undergoing an angular rotation during an impact event. Attaching the attenuator to the pintle hook alone does not prevent the attenuator from rotating during the impact event. Prior art products of this type, having a single attachment to the vehicle to the pintle hook alone, have been found, in crash testing, to provide no support for angular rotation, and to thus allow the attenuator to rotate about the pintle hook attachment during the impact. Such a uni-connection approach has thus been found to only be effective, and function properly, during a direct center line impact. Unacceptable angular rotation occurs during any angled or offset impact.
To prevent the angular rotation about the pintle hook when using a uni-connection, various manufacturers have developed additional supports in combination with the pintle hook connection. One such example is a so-called tri-support system, which utilizes two outboard supports in addition to the pintle hook support. These outboard supports, in a prior art product, comprise dual hydraulic cylinders with custom orifices which prevent compression and in turn prevent rotation of the attenuator during impact. The two outboard supports must be disconnected from the attachment pins when the attenuator is in transit. Then, upon arrival at the job site, the operator must manually attach both outboard hydraulic supports to their connection points in the backing plate. This process is complex and labor-intensive, and requires the installation of a non-factory steel plate and brackets for the cylinder pins which must be installed by the customer. Maintenance is required on a regular basis to assure that the hydraulic fluid reservoir is filled to the proper level at all times.